Schlichting jet

Schlichting jet is a steady, laminar, round jet, emerging into a stationary fluid of the same kind with very high Reynolds number. The problem was formulated and solved by Hermann Schlichting in 1933,[1] who also formulated the corresponding planar Bickley jet problem in the same paper.[2] The Landau-Squire jet from a point source is an exact solution of Navier-Stokes equations, which is valid for all Reynolds number, reduces to Schlichting jet solution at high Reynolds number, for distances far away from the jet origin.

Flow description

Consider an axisymmetric jet emerging from an orifice, located at the origin of a cylindrical polar coordinates , with being the jet axis and being the radial distance from the axis of symmetry. Since the jet is in constant pressure, the momentum flux in the direction is constant and equal to the momentum flux at the origin,

where is the constant density, are the velocity components in and direction, respectively and is the known momentum flux at the origin. The quantity is called as the kinematic momentum flux. The boundary layer equations are

where is the kinematic viscosity. The boundary conditions are

The Reynolds number of the jet,

is a large number for the Schlichting jet.

Self-similar solution

A self-similar solution exist for the problem posed. The self-similar variables are

Then the boundary layer equation reduces to

with boundary conditions . If is a solution, then is also a solution. A particular solution which satisfies the condition at is given by

The constant can be evaluated from the momentum condition,

Thus the solution is

Unlike the momentum flux, the volume flow rate in the is not constant, but increases due to slow entrainment of the outer fluid by the jet,

increases linearly with distance along the axis. Schneider flow describes the flow induced by the jet due to the entrainment.[3]

Other variations

Schlichting jet for the compressible fluid has been solved by M.Z. Krzywoblocki[4] and D.C. Pack.[5] Similarly, Schlichting jet with swirling motion is studied by H. Görtler.[6]

See also

References

  1. Schlichting, Hermann. "Laminare strahlausbreitung." ZAMM‐Journal of Applied Mathematics and Mechanics/Zeitschrift für Angewandte Mathematik und Mechanik 13.4 (1933): 260-263.
  2. Schlichting, H (1979). Boundary-layer theory, Seventh Edition, McGraw-Hill Book Company
  3. Schneider, W. (1981). Flow induced by jets and plumes. Journal of Fluid Mechanics, 108, 55-65.
  4. Krzywoblocki, M. Z. (1949). On Steady, Laminar Round Jets in Compressible Viscous Gases for Behind the Mouth. Oesterr. Ing.-Arch, 3, 373-383.
  5. Pack, D. C. (1954, January). Laminar flow in an axially symmetrical jet of compressible fluid, far from the orifice. In Mathematical Proceedings of the Cambridge Philosophical Society (Vol. 50, No. 1, pp. 98-104). Cambridge University Press.
  6. Görtler, H. (1954). Decay of swirl in an axially symmetrical jet, far from the orifice. Revista matemática hispanoamericana, 14(4), 143-178.
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